July 2022 - 11

IRRIGATION & WATER MANAGEMENT
The University of California initially developed the online tool CropManage for use on
iceberg lettuce. Since then, it has added several crops to include iceberg on both 40and
80-inch beds, Romaine lettuce on 40- and 80-inch beds, leaf lettuce, and red and
green baby lettuce. Photo: Vicky Boyd
Producers of both summer and winter broccoli can now use CropManage to fine-tune
irrigation and fertilizer applications. Photo: Vicky Boyd
stations operated by the California
Department of Water Resource,
provides ET information based
on a well-watered green lawn. To
convert it to the actual ET rate
for a specific crop - known as
the crop coefficient - Cahn said
growers would have to do lengthy
calculations. They also would have
to factor in the crop growth stage.
That's where CropManage comes
in. Based on the information
supplied by the user, program
algorithms calculate the ET crop
coefficient and recommend optimal
irrigation intervals and run times.
" We've modeled the canopy of the
different crops by taking hundreds of
pictures of the crop, " Cahn said of the
algorithms. " The more leaf area the
crop has, the more water it uses. "
CropManage nitrogen
recommendations are based on a
number of factors, including soil
samples, soil quick test results, residual
plant material in the soil, irrigation
water nitrate test results and soil
mineralization. Again, the software
factors in crop growth stage as young
plants typically don't require as much
nitrogen as larger ones or those
entering the reproductive stage.
The more information the user
can provide, the more accurate the
output. Cahn said he is confident
in the program's recommendations
because they have been groundtruthed.
Before a new crop is added,
he said farm advisors conduct
field trials to compare the online
recommendations to cooperating
growers' standard practices.
Ground-truthing a new
crop
Among those is Zheng Wang, a
UCCE vegetable and irrigation farm
advisor in Stanislaus County who has
been working with two area growers to
validate CropManage for watermelons
the past two years. Complicating
the work has been a trend toward
grafted watermelon plants, which have
different growth patterns and larger
root systems, he said. This may change
water and nutrient requirements and
timing.
Watermelons also differ from other
crops supported by CropManage
as they have a growing season that
could be up to nearly six months long
compared to processing tomatoes with
120 days. Many of the leafy greens have
only a 60-day season.
In addition, watermelons are
harvested not once but multiple times
during the season, Wang said. After
each harvest, applying additional
nitrogen and irrigation to the field
is critical to spur new growth and
continue fruit production.
" Making sure the water can be used
most efficiently without compromising
the yield is quite important, " he said.
Wang also is in his first year of
ground-truthing CropManage for
processing tomatoes on bed widths
ranging from 60 to 80 inches as well as
single- and double-row plantings.
Much of the funding to develop the
decision support tool and continue
improvements has come from
California Department of Food and
Agriculture Fertilizer Research and
Education grants, Cahn said. VGN
VGN | JULY 2022 | 11
https://www.crophesy.com
July 2022

Table of Contents for the Digital Edition of July 2022
